Effect of Hydrophobic Hydration on the Self-Assembling Behavior of Poly (l -Lactide) Homopolymers with an Ionic End Group

The investigation of hydrophobic hydration as a hydrophobic effect (HE) on the conformations and self-assembling behaviors of terminally charged poly (l-lactide) (PLLA[PPh2Me]I) in tetrahydrofuran (THF)/water with various water contents is reported. The backbone was hydrated while the ionic end group was not hydrated at a lower water content (33.3%), and consequentially PLLA[PPh2Me]I self-assembled into fibers. As the water content increased to 50.0%, ion pair end groups were hydrated and exerted a long-range dehydrating effect on the backbone, endowing chain spiralization via intramolecular C-H···O═C hydrogen bonds and leading to the formation of spheres. At 60.0% water content, the long-range effect of hydrated water on the ion pair end groups completely removed the hydration water from the backbone, and so the macromolecules possessed a certain degree of amphiphilicity and self-assembled into vesicles. The elucidation of hydrophobic hydration is desirable for improving HE-caused self-assembly and understanding biological systems.